Re: Hard Drive Destruct System?

From: Bill Unruh (unruh_at_string.physics.ubc.ca)
Date: 11/28/04 

Date: 28 Nov 2004 18:57:35 GMT

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) writes:

]In article <coas47$ijt$1@panix5.panix.com>, Al Dykes <adykes@panix.com> wrote:
]|In article <coaok5$eb0$1@canopus.cc.umanitoba.ca>,
]|Walter Roberson <roberson@ibd.nrc-cnrc.gc.ca> wrote:

]|>In practice, you can't use a single encryption over a whole drive,
]|>because you have to be able to randomly read or wrote from the middle of
]|>it without having to decrypt everything before that point (read) or
]|>re-encrypt everything after that point (write.) And directory structures

]|Offhand I can't see any problem with en/decrypting data in 512 byte
]|blocks as sectors are read/written to disk.

]If you are using the same key each time, that scheme would suffer
]a lot from "known plaintext" attacks. For example,
]All blocks of NULLs would encrypt exactly the same way, and
]the first 64 bytes of most non-text files would be relatively
]consistant amongst filetypes, allowing you a fairly good idea
]of what kind of file something was without decrypting it.

A lot less than if it was in the clear. And if they used a chaining scheme
even the nulls would not encrypt the same way.
C_i=Crypt(C_(i-1)^M_i), M_i= DeCrypt(C_i)^C_(i-1).
 Most crypto schemes are
specifically designed to resist known plaintext attacks.

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